What is "Earth-like"?

[JimC]

But how likely is a planetary environment with supercritical carbon dioxide being the main liquid?

[rainbow]

But how likely is a planetary environment with supercritical carbon dioxide being the main liquid?

Venus.

http://www.space.com/28112-venus-weird- ... ceans.html

[Brian Peacock]

Liquid methane anybody? It'll put hairs on your chest - if you can evolve a chest that is.

[Meekychuppet]

Liquid water, comparable composition, comparable atmosphere, comparable mass and gravity, hydrocarbons, you know, like er, Earth...

[rainbow]

Liquid water, comparable composition, comparable atmosphere, comparable mass and gravity, hydrocarbons, you know, like er, Earth...

Any planet with the compositions of the Earth today is unlikely to give rise to lifeforms.
Perhaps you mean the Earth as she was 4 billion years ago?
Is a moon a requirement?
Surely also a magnetic field and a tilt of 23 degrees?
Plate tectonics?


How likely is all of that?

[Brian Peacock]

We're so special. Yay us!

[Hermit]

Liquid water, comparable composition, comparable atmosphere, comparable mass and gravity, hydrocarbons, you know, like er, Earth...

Any planet with the compositions of the Earth today is unlikely to give rise to lifeforms.
Perhaps you mean the Earth as she was 4 billion years ago?
Is a moon a requirement?
Surely also a magnetic field and a tilt of 23 degrees?
Plate tectonics?


How likely is all of that?

We can only speculate. To begin with, we don't even know the size of the universe. That means we don't know how many galaxies there are, and of course we have only recently discovered exoplanets, so determining the average number of planets orbiting the stars is pure guesswork.

In the absence of sufficient empirical evidence my guess is that while it is highly unlikely that life forms more or less comparable to those we find on earth exist, it would be pretty arrogant to presume our planet to be unique in regard to having any. The argument that if there were extra-terrestrial intelligent beings one or another would have contacted us by now does not cut it for me. For one thing, they may have, and found us about as interesting as the 6000th termite mound a farmer in the Australian outback might be driving past. Expect him to maybe say "Oh look, another one." if he reacts at all. For another, it's only been just over 5000 years since humans became capable of writing things down. How often do you expect extra-terrestrials to inspect the same termite mound?

[pErvinalia]

Liquid water, comparable composition, comparable atmosphere, comparable mass and gravity, hydrocarbons, you know, like er, Earth...

Any planet with the compositions of the Earth today is unlikely to give rise to lifeforms.
Perhaps you mean the Earth as she was 4 billion years ago?
Is a moon a requirement?
Surely also a magnetic field and a tilt of 23 degrees?
Plate tectonics?


How likely is all of that?

Very fucking likely.

(I just worked it out on the back of an envelope).

[rainbow]

Liquid water, comparable composition, comparable atmosphere, comparable mass and gravity, hydrocarbons, you know, like er, Earth...

Any planet with the compositions of the Earth today is unlikely to give rise to lifeforms.
Perhaps you mean the Earth as she was 4 billion years ago?
Is a moon a requirement?
Surely also a magnetic field and a tilt of 23 degrees?
Plate tectonics?


How likely is all of that?

Very fucking likely.

(I just worked it out on the back of an envelope).

Please show your workings.

[pErvinalia]

The dog ate it.

[JimC]

rainbow wrote:

Any planet with the compositions of the Earth today is unlikely to give rise to lifeforms.
Perhaps you mean the Earth as she was 4 billion years ago?

There may be some truth in this, but it will mostly be due either to the fact that the Earth is currently highly polluted with biogenic oxygen, and/or that any poor new beastie would be quickly gobbled up by something voracious...

[rainbow]

rainbow wrote:

Any planet with the compositions of the Earth today is unlikely to give rise to lifeforms.
Perhaps you mean the Earth as she was 4 billion years ago?

There may be some truth in this, but it will mostly be due either to the fact that the Earth is currently highly polluted with biogenic oxygen, and/or that any poor new beastie would be quickly gobbled up by something voracious...

Tigers don't eat trees, so I think the argument falls down. Why would new beasties be at all tasty to existing life forms?
The main reason I believe that life doesn't appear under present Earth conditions is that temperatures are too low for organic reactions. Almost no organic chemistry takes place on Earth outside of biology and human directed synthesis.. What does take place is inevitably destructive, oxidation due to the biogenic oxygen you mention, and C-C bond breakage due to UV light.
The reason biochemistry works is that enzymes are able to allow these organic reactions to overcome activation energies. In organic synthesis we normally work at higher temperatures, pressures and we use highly reactive reagents (which do not easily survive in nature)

[JimC]

Any new life form would arise as a simple carbon-based replicator, that existing bacteria would feast on - they are rather catholic in their tastes...

I don't think it's so much the temperature, but in any case there are hot springs and black smokers a-plenty; all of them, however, with existing microbial populations, whether or not the local environment has oxygen. It's possible that new replicators have formed many times since the original explosion of life, but were quickly cannibalised by their elder brethren. You of all people should understand that...

[pErvinalia]

[rainbow]

Any new life form would arise as a simple carbon-based replicator, that existing bacteria would feast on - they are rather catholic in their tastes...

You know this how exactly?
Please describe this simple carbon-based replicator, and what metabolic processes it would employ.

I don't think it's so much the temperature, but in any case there are hot springs and black smokers a-plenty; all of them, however, with existing microbial populations, whether or not the local environment has oxygen. It's possible that new replicators have formed many times since the original explosion of life, but were quickly cannibalised by their elder brethren. You of all people should understand that...

Not all organic compounds are food. In fact a very small subset of the chemicals we recognise as organics are biodegradable.